Chemistry and Physics. 387 



points of which are situated on the surface of the sethereal shell, 

 but freely moveable within it. The di-poles themselves can 

 rotate freely round their middle point. The carbon atom has a 

 greater attraction for positive than' for negative electricity and 

 the positive pole of a valence is slightly stronger than the nega- 

 tive pole. The following facts, it will be observed, become ex- 

 plicable upon the above hypothesis: (1) why the four valences 

 take up the position of a regular tetrahedron ; (2) why they can 

 be diverted from this position ; (3) why the valences of one and 

 the same carbon-atom cannot combine together, while the valen- 

 ces of different carbon-atoms can do so ; (4) why there are two 

 kinds of single binding (a) a stable one and (b) one allowing free 

 rotation ; and (5) why free rotation ceases in cases of double or 

 triple-binding. — JBer. Berl. Chem. Ges., xxi, 946, March, 1888; J. 

 Chem. Soc, liv, 549, June, 1888. g. f. b. 



7. The Chemical Analysis of Iron; by Andrew Alexander 

 Blair. 282 pp. 8vo, Philadelphia, 1888. "(J. B. Lippincott Com- 

 pany). — In this volume the author has given a full account of 

 the methods employed in the analysis of iron and steel, iron ores, 

 slags, limestone, clay, sand, the fuels, furnace gases. It is ex- 

 haustive in method, describing the apparatus and the methods 

 of making reagents as well as the details of the quantitative 

 processes by which the various constituents are determined. The 

 execution of the work as regards printing, cuts, etc., is unusually 

 good, and fully up to the excellence of the subject matter. 



8. Biterference of Electro-magnetic Waves. — Professor Fitz- 

 gerald, Vice President of the Mathematical and Physical sections 

 of the British Association at the late meeting at Bath, England, 

 thus speaks of Hertz's work. " There are some difficulties sur- 

 rounding the complete interpretation of some of Hertz's experiments. 

 The conditions are complicated, but I confidently expect that they 

 will lead to a decision on most of the outstanding questions on 

 the theory of electro-magnetic action. There is no doubt that 

 he has observed the interference of electro-magnetic waves quite 

 analogous to those of light, and that he has proved that electro- 

 magnetic actions are propagated in air with the velocity of light. 

 By a beautiful device Hertz has produced rapidly alternating 

 currents of such frequency that their wave-length is only two 

 meters. These waves are propagated three hundred thousand 

 kilometers in a second. To detect them he made use of the 

 principle of resonance, and constructed a circuit whose period of 

 vibration for electric currents was the same as that of his genera- 

 ting vibrator, and he was able to see sparks, due to the induced 

 vibration, leaping across a small air space in this resonant circuit. 

 He has been able to observe the interference between waves in- 

 cident on a wall and the reflected waves. His generating vibrator 

 was placed several wave-lengths from a wall and the receiving 

 resonant circuit was placed between the generator and the wall. 

 In the air space he was able to observe that at some points there 

 were hardly any induced sparks, but at other and at greater dis- 



